It is known, for example from European Patent No EP 0987431 (Delphi Technologies Inc.), to provide a fuel injector with two independently operable valve arrangements for controlling fluid pressure within the injector, as shown in FIG. 1. The valve arrangements are arranged to control injection by an injector valve needle 10. Fuel is supplied to an injector delivery chamber 11 from a high pressure pump chamber 12, via a fuel supply passage 14, and movement of the valve needle 10 away from the seating permits fuel to flow from the injector delivery chamber 11 through one or more outlet openings 16 into the engine or other combustion space.
A first one of the valve arrangements is known as the control valve arrangement, or the nozzle control valve 18, and includes a control valve member which is operable to control fuel pressure in a control chamber 20. When the nozzle control valve 18 is in a first (open) position a communication path is opened between the control chamber 20 and a low pressure drain, and when the nozzle control valve 18 is in a second (closed) position the communication path is closed. The nozzle control valve member is biased into the closed position by means of a spring (not shown). There is a constant supply of high pressure fuel into the control chamber 20 so that when the nozzle control valve 18 is in the closed position, fuel pressure in the control chamber 20 is caused to increase.
A second one of the valve arrangements is a drain or spill valve arrangement 24 which controls whether pressurisation of fuel takes place within the pump chamber 12. The spill valve 24 serves to control whether the pump chamber 12, and hence the fuel supply passage 14, communicates with the low pressure drain, or whether the communication path between the fuel supply passage 14 and the low pressure drain is closed. When the spill valve 24 is in a first (open) position the fuel supply passage 14 communicates with the low pressure drain and when the spill valve 24 is in the second (closed) position communication between the fuel supply passage 24 and the low pressure drain is closed. The spill valve is biased into the open position by means of spring (not shown).
A surface associated with the valve needle 10 is exposed to fuel pressure within the control chamber 20, thereby applying a force to the valve needle 10 to urge the valve needle 10 towards its seating and closing the flow of fuel to the outlet openings 16. In this position, injection of fuel into the engine or other combustion space does not occur. In order to commence injection, the nozzle control valve 18 is actuated such that the control valve member is moved into its open position, thereby causing fuel pressure within the control chamber 20 to be reduced. The force urging the needle 10 towards its seating is therefore reduced and fuel pressure within the injector delivery chamber 11 acts on thrust surfaces of the valve needle 10 to lift the valve needle away from its seating to permit fuel to flow through the injector outlet openings 16.
In order to terminate injection, the nozzle control valve 18 is de-actuated such that the control valve member is moved into its closed position under the spring force, thereby closing the communication path between the control chamber 20 and the low pressure drain. The force acting on the valve needle 10 due to fuel pressure within the control chamber 20 is therefore increased, causing the valve needle 10 to be urged against its seating to terminate injection. The nozzle control valve 18 is therefore operable to control the pressure differential between the fuel in the control chamber 20 and the fuel in the injector delivery chamber 11, that is to say the differential in the pressure acting to close the needle 10 and the pressure tending to act to open it. In addition to the pressure of fuel in the control chamber 20 tending to urge the valve needle 10 to close, a closing spring 22 is provided to assist the aforementioned closing force.
Another method of terminating injection is to use the spill valve 24. When the spill valve 24 is in its open position, fuel flows from the fuel supply passage 14 and the injector delivery chamber 11 to the low pressure drain such that fuel pressure within the fuel supply passage 14 and the injector delivery chamber 11 is reduced. The resulting pressure differential between the control chamber 20 and the injector delivery chamber urges the valve needle 10 against its seating, closing the flow path to the outlet openings 16 and terminating injection. When the spill valve 24 is moved into its closed position and high pressure fuel is re-established  within the injector delivery chamber 11, the valve needle 10 is caused to lift from its seating to commence injection.
The injector is provided with a twin, double pole actuator arrangement to control both the nozzle control valve 18 and the spill valve 24. The actuator includes first and second windings 26, 28, or solenoids, energisable to control movement of first and second armatures, 31, 32, respectively (i.e. a double pole actuator including the winding 26 controls the nozzle control valve 18, and a double pole actuator including the winding 28 controls the spill valve 24).
The first armature 31 is coupled to the nozzle control valve member so that energisation of the first winding causes the first armature 31, and hence the nozzle control valve member, to move between its closed and open positions. Energisation of the actuator thus causes the nozzle control valve member to move into the open position, whilst de-energising of the actuator causes the spill valve member to move into the closed position (under the influence of the spring).
The second armature 32 is coupled to the spill valve member so that energisation of the second winding 28 causes the second armature 32, and hence the spill valve member, to move between its open and closed positions. Energisation of the actuator causes the spill valve member to move into the closed position, whilst de-energising of the actuator causes the spill valve member to move into the open position under the influence of the spring.
In other injector designs, the nozzle control valve 18 is removed so that only a spill valve is provided. It is known here to provide an electromagnetic actuator having a single winding to control operation of the spill valve 24.
In another known injector, such as that described in EP 1120563 A (Delphi Technologies, Inc.), a nozzle control valve 18 and a spill valve 24 are provided as in FIG. 1 but the nozzle control valve is controlled by means of a single pole actuator, not a double pole actuator (i.e. there is no outer pole). An injector of this type is shown in FIG. 2. As in EP 0987431, the spill valve is controlled by means of a double pole actuator.
It is desirable to reduce the eddy current effects that exist in the actuator cores of the injectors of the aforementioned type. There is also a requirement to improve the flux density capability of the actuator.
It is one aim of the invention to provide an improved actuator arrangement which addresses these issues.